What is Constant Mesh Gearbox? Construction And Working Principle


A constant mesh transmission is that a form of manual transmission in which sliding gears from the sliding mesh gearbox is replaced with the constantly meshed combines of gears and also the new shifting devices named dog clutches square measure introduced which helps in transmittal the desired output to the most shaft by creating contact with the acceptable pair of the meshed gears.

Constant Mesh Gearbox
Constant Mesh Gearbox

A constant mesh transmission typically comes with 4 forward speeds and 1 reverse manual transmission configuration.

Why will we want Constant Mesh Transmission?

The introduction of initial transmission system i.e. sliding mesh transmission was an excellent success in cars trade as currently there was a system which might offer needed torsion and speed ratios want by the vehicle to face the road challenges however still there have been several vital issues with this gear that raised the question on its effectiveness and responsibility. the issues long-faced were as follows-

The shifting of gears wasn’t a simple task because the shifting needed a special technique that wasn’t in any respect everybody’s cup of tea, a talented driver was needed for driving such vehicle, the special technique needed being Double-de-clutching.
Note – Double-de-clutching- it’s the technique because the name indicates that needed double engagement and disengagement of clutch for shifting one gear.

Constant Mesh Gearbox
Constant Mesh Gearbox

f i.e. once driver needs to shift the gear he initial presses the clutch pedal and produce the gear to the neutral, than once more he releases the clutch pedal and accelerate so as to extend the speed of the lay-shaft in order that the meshing of applicable gear will occur, save for he presses the clutch pedal and produce the gear lever to the desired gear and unleash the clutch pedal and at last the desired gear is obtained.

Since the gears are to be meshed square measure in continuous rotation with a completely different speed than the meshing of those gears will cause breakage to the gear teethes or continuous wear and tear is there.
The shifting of gears could be a terribly clamant method.

High maintenance is needed as slippy and meshing of gears causes resistance to wear of shafts and gears.


Constant Mesh Gearbox
Constant Mesh Gearbox


  1. Clutch Shaft.
  2. Lay Shaft or counter Shaft.
  3. Main Shaft.
  4. Dog clutch.
  5. Gears.

There are different types of gears with both spur and helical gears like:

  1. Clutch gear.
  2. First gear.
  3. Second gear.
  4. Reverse gear.


In Constant Mesh Gearbox gearbox, all gears of the main shaft are in constantly meshed with the corresponding gears of the layshaft or countershaft. Too dog clutches are provided on the main shaft: one between the clutch gear and the second gear; and the other between the first gear and reverse gear. The main shaft is made splined and all the gears are free to move on it. Dog clutches can slide on the main shaft and rotates with it. All the gears on the countershaft are permanently fixed with it.

When the left dog clutch is made to slide to the left with the help of the gear shift lever, it meshes with the clutch gear and the top speed gear is obtained. When the left dog clutch meshes with the second gear on the main shaft, the second speed gear is achieved. Similarly, by sliding the right-hand dog clutch to the left and right, the first speed gear and reverse gear are obtained respectively In this type of gearbox, because all the gears are in constant mesh, they are safe from being damaged and unpleasant grinding sound does not occur while engaging and disengaging them.

From the video below you can watch the Constant mesh gearbox manual transmission working animation:

Constant-mesh gearbox manual transmission working animation

Also, Read These Posts

  1. What are All Wheel Drive(AWD) and Four Wheel Drive(4WD) cars?


Creative Blogger And Automobile Engineer.

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